One of the more important constraints to the continued growth of air traffic is the related concern regarding aircraft noise. This concern has resulted in increasingly stringent noise restrictions for airports. During aircraft take-off, the dominant aircraft noise source is generally the propulsion noise from the engines of the aircraft. During aircraft approach and landing, airframe noise becomes a prominent component on par with the engine noise. This airframe noise is caused by the interaction of the unsteady and typically turbulent airflow with the aircraft structures. The sound radiated from the side edge of a partial-span flap is one of the major contributors to airframe noise during aircraft approach and landing.
Previous approaches for reducing noise at the flap side edge have included protruding brushes and structural links between flap side edge and the main wing element. Although use of brushes at flap and slat tips has generally been effective for reducing noise produced by these components, the use of brushes has negative side effects. These side effects include degradation in aerodynamic performance of the high-lift wing during landing, and alteration of stall characteristics of the aircraft due to reduction in the maximum lift coefficient.